The present invention relates to oil separation systems for oil field facilities. More particularly, the present invention is a method and apparatus for the continuous separation of oil from solid and liquid contaminants at the site of oil field drilling operations.
The current method for separating oil from solid and liquid contaminants involves the use of a multiplicity of open-top separation tanks in which contaminated oil withdrawn from the well is allowed to settle out or separate by gravity. As contaminated oil is withdrawn and directed to the first tank, the heavier solids fall to the bottom of the first tank and lighter oil/water overflows a weir or a series of weirs and continues on to subsequent tanks. In the second and successive tanks, the heavier water tends to gravitate to the lower portion of a tank, is pumped off, cleaned and, usually, reinjected into the well head. Slight variations on the process exist, such as the use of one large tank with a series of overflow weirs, but generally the above description is the state of the art.
A significant disadvantage of current technologies is that increasing flow rates from the wellhead necessitate the addition of tanks in order to provide additional settling time. The more tanks required, the more crowded and confused becomes the well site. Serious environmental problems are created as trenches are dug around the tanks to handle possible overflows and splashing. The greater the number of open tanks at the site, the greater the chances of fire and ambient gas problems. The gas problems are inherent with open tanks because the lighter, more volatile hydrocarbons evaporate to the region immediately above the oil surface layer in the tanks. The greater the number of tanks, the greater the overall open, exposed surface area of oil, and the greater the level of ambient gases.
Therefore, any system which can reduce the number of tanks required and at the same time handle a greater input flow rate resolves long standing problems in the industry. The present invention is such an improvement.
Another major problem with existing separation systems relates to downtime. Anytime flow from the wellhead must be interrupted, there is a corresponding loss of production and profit. In some cases, depending on the selling price of oil, the cost of downtime may be $2,000 per hour. Assuming that the flow rates are controlled and the oil separation system is balanced, downtime, except for mechanical/electrical equipment failure, may be minimized, but not eliminated in existing systems. The reason for this downtime is that the solid contaminants (also known as drill cuttings or shale) in the first settling tank gradually build up and reduce the effective dwell time of the contaminated oil in the tank. Further, as the solids build up in the first tank, the bottom of the tank is effectively "raised" and splashing of incoming liquid increases, increasing the safety hazards to man and the environment.
At some point in the operation of existing separation systems, the incoming oil flow must be stopped and the first separation tank cleaned of the built up solids. Normally any head of liquid is pumped off of the top of the solid material by use of a flexible suction line and a portable pumping system. The solid material is then manually or mechanically shoveled out of the tank and disposed of at a remote location. Alternatively, clean drilling fluid is combined with the drill cuttings and transferred to the on-site shaker assembly for separation at considerable cost. In any case, the existing procedures call for the curtailment of separation operations during the removal of solid cuttings from the settling tanks.
The present invention provides a method and apparatus for allowing the solid cuttings to be removed from the bottom of the settling tank without interruption of the continuous separation operation. Therefore, with the present invention, it is possible to eliminate expensive downtime currently necessitated by the removal of solid contaminates from the settling tanks.
When the unique features of the present method and apparatus are combined, increased flow rates and flow durations may be achieved with fewer settling tanks, reduced safety hazards, and far less negative impact on the environment at the well site. Thus, the present invention solves long-standing problems and meets long-felt needs in oil field operations.